1. Field of the Invention
The present invention relates to a thin film transistor structure having a gate electrode, a source electrode, a drain electrode, wirings connected to the electrodes, and a semiconductor layer, a method of manufacturing the same, and an electronic device having the thin film transistor structure.
2. Description of the Related Art
In recent years, an active matrix driving method is introduced to many electronic devices typified by a display device such as a liquid crystal display (LCD). In the driving method, a thin film transistor (TFT) is used as an element for switching (pixel selection).
Among them, recently, attention is paid to a TFT using an organic semiconductor layer as a channel layer, and the TFT is called an organic TFT. In the organic TFT, a channel layer is formed by coating, so that cost is low. Since the channel layer is formed at a temperature lower than that in vapor deposition, the organic TFT is mountable on a low-heat-resistance flexible plastic film and the like.
A TFT is used for an electronic device as a part of a TFT structure, and the TFT structure has the TFT and a wiring connected to the TFT. The TFT includes, in addition to the channel layer, a gate electrode, a gate insulating layer, a source electrode, and a drain electrode. Wirings include a gate electrode wiring, a source electrode wiring, and a drain electrode wiring connected to the gate electrode, the source electrode, and the drain electrode, respectively.
To assure the performance of an electronic device using the TFT structure, it is necessary to prevent short circuit between the gate electrode for applying gate voltage and the source and drain electrodes for applying signal voltage (inter-electrode short-circuit). When an inter-electrode short-circuit occurs, a serious operation defect is caused. Causes of occurrence of the inter-electrode short-circuit include a pin hole which is opened in the gate insulating layer and a foreign matter which enters inside thereof.
To prevent the inter-electrode short-circuit, various examinations are being conducted. Concretely, the gate insulating layer in a region where the gate electrode, and the source electrode and the drain electrode overlap is made thicker than that in the other region (see, for example, Japanese Unexamined Patent Application Publication No. 2002-094071).